This application claims priority under 35 U.S.C. xc2xa7119 to Great Britain Patent Application No. 0024666.0 filed Oct. 9, 2000, and to Great Britain Patent Application No. 0025534.9 filed Oct. 17, 2000.
Not Applicable.
Not Applicable.
1. Field of Invention
The present invention relates to a chain drive assembly for elevating a load particularly, but not exclusively, to such a drive assembly for a leisure ride such as, for example, a roller-coaster.
2. Description of Related Art
A schematic representation of an inclined section of a typical leisure ride is shown in FIG. 1. A vehicle carriage for carrying passengers is driven up the incline along a track to a summit by a chain drive assembly. The track then drops steeply from the summit so that as the vehicle carriage follows the track it descends under its own gravity. The chain drive assembly comprises an endless loop bush or roller chain that is disposed under the track and is driven at a lower end of the inclined section by a drive box assembly comprising a drive wheels several guide and tensioning wheels and a suitable motor. The chain is supported on a bearing surface and passes up the incline, around a sprocket wheel at the summit before returning to the drive box assembly. The underside of the carriage has a depending dog which engages in a space between adjacent links of a chain so as to enable the chain to drive the carriage uphill towards the summit. It will be appreciated that, in use, the stretch of chain that extends from the carriage, around the summit sprocket wheel and returns to the drive box, is under tension. It will also be appreciated that in certain rides there may be several vehicle carriages connected together in a train, with only the lead carriage having a dog for engagement with the chain.
There is generally a separate drive system that is responsible for moving the vehicle carriage substantially in a horizontal direction from a starting position where passengers embark to a position where it engages the chain at the commencement of the inclined section.
In contemporary times there is a trend toward rides that are both faster and larger, in the sense that they can carry a greater number of passengers at once, have higher summits and therefore longer descents. As a result, the speed and loads of such leisure rides lave increased dramatically in recent years. For example, in the early 1980s the speed of such rides was typically around 1 to 1.4 m/s and the load capacity around 40 kN whereas now the demand is for rides having speeds in excess of 3 m/s with a load capacity of around 120 kN. These increases put greater demands on the chain and there are several reasons why a conventional cranked link chain is no longer appropriate.
First, the greater the lift height (the height through which the chain must lift the carriage), the load capacity and the speed of the chain, the larger the chain must be. The larger the chain, the heavier it is and therefore, in use, it has to work against its own weight in addition to the load of the carriage and passengers.
Second, leisure ride designers would like the dog of the lead carriage to be larger for safety reasons. In order to accommodate this it is necessary to increase the chain pitch thereby providing a larger gap between adjacent links for the dog to be received. However, a chain with increased pitch requires the drive and driven sprockets to have larger diameters. The corresponding reduction in the number of teeth on the sprockets (as a result of the increased chain pitch) effects an increase in what is known as xe2x80x9cthe polygonal effectxe2x80x9d during the meshing of the chain with the teeth of the sprocket. This effect describes the uncontrolled and rapid movement of the chain links relative to the sprocket teeth during meshing and unmeshing of the chain with the sprocket wheel. The movement arises from the fact that the pitch line of the chain comprises a plurality of straight lines or chords that combine to form part of a polygon rather than a circle (as would be the case for a flexible belt). The rapid and uncontrolled movement of the chain links results in them impacting upon the sprocket with a high velocity thereby generating unwanted noise.
Third, the increased load on the chain results in increased pressure on the bearing surfaces of the chain and consequently the chain is susceptible to increased wear resulting in a reduction in its working life. A significant part of chain wear in a leisure ride drive occurs during its articulation under load around the sprocket (or sprockets) at the summit.
Fourth, the speed of a chain is limited by the centrifugal force of the links as they pass around the sprockets. It will be appreciated that the magnitude of this force on a given chain link increases with its mass.
It is an object of the present invention to obviate or mitigate the aforesaid disadvantages and to provide for a chain drive assembly that is capable of operation with increased loads and at increased speeds in comparison to existing drives.
A known type of escalator chain drive comprises a step chain having a pair of parallel, laterally spaced chain strands that are interconnected by transversely extending elongate axles. Each of the chain strands comprises a plurality of chain links joined end-to-end in an articulating relationship. The links of the chain each have a lower surface on which there is defined a plurality of teeth. The step chain is driven on each side by synchronized roller chains, the teeth of the step chain links being received in spaces between rollers of the drive chains.
According to a first aspect of the present invention there is provided a chain drive assembly for elevating a load, the assembly comprising an endless loop lift chain having a plurality of links, and a plurality of drive members, the chain links comprising a pair of laterally spaced outer link members pivotally connected to at least one outer link member disposed at least in part between the outer link members, at least one of the link members of each link having a plurality of formations for engagement with complementary formations on the drive members, the drive members being disposed so as to engage the formations at a rectilinear portion of the chain loop so as to drive the chain in a longitudinal direction, the inner and outer link members being arranged to define an opening designed to receive a projection on said load.
The chain assembly of the present invention allows a significant part of the load to be carried by the drive members rather than by the chain itself. Since the drive members drive the chain at a rectilinear portion of the chain loop the requirement for the chain to be entrained over drive and driven sprockets is eliminated. Instead, the chain can simply pass over a guide wheel or other guide members at each end of the loop. In view of the fact that the load is carried by the drive members at the rectilinear portion of the lift chain loop, the chain links no longer articulate under significant load and wear is thus reduced considerably. This reduction in wear virtually eliminates the requirement to lubricate the chain. Other advantages include: the chain may be made lighter so the chain speed is not restricted by the centrifugal action of the chain links around the sprocket; there is no need for a polymer bearing surface under the lift chain; and the conveyor chain can be arranged to have an initial stretch that is not inclined.
In one preferred embodiment of the design the outer link members each have said plurality of formations. In an alternative but equally preferred design only the inner link member has said plurality of formations.
The formations are preferably in the form of a row of teeth but may be defined by other profiles.
The link members are ideally in the form of link plates.
An upper surface of the inner link member is preferably shaped so as to receive said projection on said load.
In one preferred embodiment there are provided bearing members outboard of said outer link members, the bearing members being guided along a track so as to prevent lateral movement of chain. The bearing members are preferably rollers disposed on pins of said chain but could alternatively be thrust pads or blocks or the like. The rollers are preferably at least partially enclosed by the guide track which may be of channel-shaped cross-section.
In a preferred embodiment the drive member is in the form of a roller chain having a plurality of links between which are defined clearances into which the formations of the lift chain are received. In alternative embodiment the drive member may be a toothed belt or wheel.
In the instance where the formations are provided on the outer link of the lift chain two drive roller chains are provided, one on each side of the lift chain.
The inner links may comprise a central section of a depth substantially equal to the depth of the outer link and end sections of reduced depth.
According to a second aspect of the present invention there is provided a leisure ride having an inclined track on which a carriage is driven by a chain drive assembly as defined above, the carriage having a projection for engagement in one of said openings of the chain.